Treatment of aqueous systems

ABSTRACT

A method is described for preparing in-situ a substantially maleic acid copolymer for a treatment additive for aqueous systems, in which crystal habit modification properties are prioritized; for aqueously preparing a substantially poly-maleic additive through in-situ formation of maleic acid copolymer so that mono-carboxylic acids, non-ionic functional groups, and terminal hydroxyl groups are also formed during polymerization; and for applying such additives for treatment of aqueous systems. Treatment agents resulting from these processes are also described.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and is a divisional of U.S.Pat. Application 17/743,603, filed May 13, 2022, which is a continuationof U.S. Pat. Application Number 15/937,990, filed Mar. 28, 2018, whichis a divisional application of U.S. Pat. Application No. 14/525,216,filed Oct. 28, 2014, all of which are incorporated herein by referencein their entireties.

BACKGROUND OF THE INVENTION

The present invention relates to treating aqueous systems to prevent orremediate problems of mineral scale deposition and buildup. Fields ofexpected application include, without limitation, water treatment,industrial aqueous systems treatment, cooling water systems, boileroperation, thermal and reverse osmosis desalination activities, gas andoilfield operations, municipal and wastewater treatment, pulp and paperprocesses, and detergent/cleaning applications.

Various types of contaminants in an aqueous system under a variety ofconditions can cause problems such as corrosion, microbiologicalcontamination, or mineral scaling, in which contaminants precipitate outof solution in the system and form undesirable scale deposits on systemsurfaces. Of particular interest to the present invention is thechallenge of scale management. Polymer mediated scale control techniqueshistorically involve a variety of mechanisms that are generally known inthe art, including, for example, threshold inhibition, sequestration,chelation, stabilization, particulate dispersion, and crystal habitmodification. These mechanisms are discussed and defined below.

Threshold inhibition involves extending the solubility of an otherwiseinsoluble salt beyond normal saturation limits using an additive whichfunctions at sub-stoichiometric levels. This sub-stoichiometricfunctionality differentiates treatment additives such as polymers andphosphonates from materials that function according to strictstoichiometric ratios such as Ethylenediaminetetraacetic acid (EDTA).Threshold inhibition is often a temporary effect. For example, ifuninhibited water takes 60 seconds to begin precipitating calciumcarbonate in a given set of conditions (such as pH, temperature,concentrations of calcium and carbonate, etc.), the same water may betreated to extend this time to one hour through a threshold inhibitionadditive. The extent and duration of threshold inhibition may be relatedto a variety of factors or conditions, including without limitation thedriving forces for precipitation (pH, temperature, concentrations ofscale-forming ions, etc.), the particular efficacy of a selectedthreshold inhibition additive, other water impurities (dissolved orsuspended), rate of water concentration or evaporation, and frequency ofadditive dosage.

Sequestration can be another important function of treatment additives,particularly of many polymers and phosphonates. Sequestration is thecomplexation of a metal ion such that the ion does not retain itsoriginal reactive properties. Unlike threshold inhibition, sequestrationdoes not connote either stoichiometry or specific functionality. Somephosphonate or polymer additives commonly used for mineral scale controlcan sequester ions such as calcium, magnesium, and barium, preventingthem from forming insoluble complexes with compounds such as carbonateand sulfate.

A chelate is a coordination compound in which a central metal ion suchas Ca²⁺ is attached by coordinate links to two or more non-metal atomsin the same molecule, called ligands. Thus, a chelating agent is anadditive that links to a metal ion at two or more points within theagent molecule. In practice, polymers such as polycarboxylates andsulfonated copolymers act as chelating agents with most multi-valentions due to the multiple binding sites along the polymer’s backbone. Incommon usage, chelation further implies a more permanent or substantiverelationship between the ion and the ligand and refers to stoichiometricrelationships between the metal ion and the ligand.

Stabilization may refer to two distinct mechanisms. In colloidalstabilization, precipitation in a fluid (such as water) occurs, but thepolymer additive prevents agglomeration of particles larger than onemicron in size. These particles are thus stabilized via electrostaticinteractions with the polymer and remain suspended throughout the waterphase. These sub-micron particles are typically invisible to the nakedeye. A notable exception to this is stabilized iron particles, which canbe visible due to the orange-brown color associated with most oxidized(Fe³⁺) iron complexes. Colloidal stabilization can fail due to physicalor chemical changes in the fluid that result in particulateagglomeration beyond one micron in size and bulk settling of theprecipitate. The alternate usage of “stabilization” is as a synonym forsequestration, where a coordination complex between a polymer additiveand soluble ions, or surface interaction between polymer and formingcrystal lattices, occurs, preventing precipitation.

Particulate dispersion is a suspension of particulates in an aqueoussolution. Particulate dispersion involves a mixture of finely dividedparticles, called the internal phase (often of colloidal size), beingdistributed in a continuous medium, called the external phase. These canbe inorganic (e.g., calcium carbonate), organic (e.g., biomass), or amixture of the two. Polymer composition and molecular weight (Mw) arekey determinants in deriving functionality for effective particulatedispersion.

The final mechanism discussed here in relation to scale control iscrystal habit modification. A crystal habit is defined as the normalsize and shape of a precipitated substance in a given set ofenvironmental conditions. FIGS. 1A through 1E illustrate simplisticallya formation process of crystals such as calcium carbonate, and thecrystals’ subsequent deposition onto surfaces. The formation of crystalssuch as calcium carbonate and their subsequent deposition onto surfacesfollow a process, simplified here for clarity, of nucleation(illustrated in FIG. 1A), lattice formation and propagation (illustratedin FIG. 1B), bulk precipitation (illustrated in FIG. 1C), and surfacedeposition (illustrated in FIGS. 1D & 1E). Modification of crystal habitinvolves introducing a “poison” or contaminating additive that disruptsnormal lattice formation. This, in turn, yields crystals tending eitherto re-dissolve or to precipitate in abnormal forms that deviate from thesubstance’s untreated crystal habit. This effect tends to reducecohesion of the crystals to each other (dispersion) and adhesion ofcrystals to system surfaces (scaling).

Although the general mechanisms described above are known and, to somedegree, understood in the art of treating aqueous systems, the exactfunctionality of treatment additives often is not. In practice, variouspolymer additives often are viewed as single-purpose. In application,threshold inhibition is often prioritized as the most important scalecontrol mechanism, to the relative neglect of other mechanisms. Byfocusing more precisely on additive functionalities, it is possible totake advantage of interrelationships among these scale controlmechanisms, and improvements can be achieved in the art of treatingaqueous systems.

An object of the invention is to achieve improved treatment of aqueoussystems by re-prioritizing the scale treatment mechanisms targeted. Afurther object is to prepare a substantially poly- maleic additivethrough in-situ formation of maleic acid copolymer so thatmono-carboxylic acids, non- ionic functional groups, and terminalhydroxyl groups are also formed during polymerization. Improvedtreatments may then be applied to aqueous systems to achieve variousimprovements in scale prevention or remediation.

BRIEF SUMMARY OF THE INVENTION

In a basic embodiment of the invention, a method is described toprioritize crystal habit modification in selecting a treatment additivefor aqueous systems. In further illustrative embodiments, polymermaterials are specified which exhibit improved crystal habitmodification properties and other advantages. Also, methods arespecified for preparing and applying improved polymer additives toprevent, reduce, or remediate scale formation or precipitation inaqueous systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be better understood with reference to the followingfigures and detailed description.

FIG. 1A depicts nucleation (diffusion from solution to solids). FIG. 1Billustrates lattice formation and propagation (disorder to order). FIG.1C depicts macro calcite formation, bulk precipitation, and exhaustionof soluble ions. FIG. 1D illustrates surface deposition via adhesion toa metal surface. FIG. 1E illustrates surface deposition via adhesion toa tube/pipe interior.

FIG. 2A illustrates a typical understanding of mechanisms of polymerfunctionality. FIG. 2B depicts an improved understanding whichprioritizes crystal habit modification as a first-order concern intreating aqueous systems.

FIG. 3A conceptually depicts sequestration and chelation in polymerinteractions with divalent calcium in an illustrative case. FIG. 3Bconceptually depicts sequestration, chelation, crystalloid formation,and stabilization.

FIG. 4A is a conceptual depiction of polymer adsorption onto a formingcrystal lattice. FIG. 4B further illustrates dimensions of inhibitedcrystal growth. FIG. 4C depicts re-dissolution of an unstable crystallattice. FIG. 4D shows bulk precipitation with crystal habitmodification of the bulk precipitate.

FIG. 5A illustrates crystal habit modification in bulk precipitatesrelative to surfaces in a system. FIG. 5B illustrates crystal habitmodification in bulk precipitates relative to surfaces in a system.

FIG. 6 is a table of simplified polymer functionalities for some commonmineral scales and deposits.

FIG. 7A illustrates polymer rigidity under stressed water conditions foran enhanced copolymer according to an embodiment of the invention. FIG.7B illustrates polymer rigidity under stressed water conditions formono-carboxylic acid polymers such as polyacrylic acid.

FIG. 8 is a table detailing experimental conditions.

FIG. 9A illustrates compound microscopy showing exclusive formation ofcalcite in a blank sample without polymer treatment at 10Xmagnification. FIG. 9B illustrates compound microscopy showing exclusiveformation of calcite in a blank sample without polymer treatment at 40X.

FIG. 10A illustrates a Scanning Electron Micrograph (SEM) showing auniform calcite (cubic calcium carbonate) precipitate at 250Xmagnification. FIG. 10B illustrates a Scanning Electron Micrograph (SEM)showing a uniform calcite (cubic calcium carbonate) precipitate at1500X.

FIG. 11A illustrates compound microscopy of results of PMA treatment at15 mg/l at 40X magnification. FIG. 11B illustrates SEM micrographresults of PMA treatment at 15 mg/l at 1500X magnification. FIG. 11Cillustrates compound microscopy results of PMA treatment at 30 mg/l at40X magnification. FIG. 11D illustrates SEM micrograph results of PMAtreatment at 30 mg/l at 1500X magnification.

FIG. 12A illustrates compound microscopy results of MOP treatment at 15mg/l at 40X magnification. FIG. 12B illustrates SEM micrograph resultsof MOP treatment at 15 mg/l at 1500X magnification. FIG. 12C illustratescompound microscopy results of MOP treatment at 30 mg/l at 40Xmagnification. FIG. 12D illustrates SEM micrograph results of MOPtreatment at 30 mg/l at 1800X magnification.

FIG. 13A illustrates compound microscopy results of treatment at 15 mg/lusing an enhanced copolymer at 40X magnification. FIG. 13B illustratesSEM micrograph results of treatment at 15 mg/l using an enhancedcopolymer at 1500X magnification. FIG. 13C illustrates compoundmicroscopy results of treatment at 30 mg/l using an enhanced copolymerat 40X magnification. FIG. 13D illustrates SEM micrograph results oftreatment at 30 mg/l using an enhanced copolymer at 1500X magnification.

FIG. 14 is a chart comparing threshold inhibition performance betweenPMA and an enhanced copolymer under severe calcium test conditions.

FIG. 15 is a nuclear magnetic resonance (NMR) spectrograph of a priorart material, as copied from U.S. Pat. 5,135,677 (Yamaguchi et al).

FIG. 16 is an NMR spectrograph of an enhanced copolymer.

FIG. 17 shows chemical structures and reactions related to an enhancedcopolymer.

DETAILED DESCRIPTION

Known methods and additives have tended to emphasize thresholdinhibition as a primary mechanism in treating aqueous systems.Illustrative embodiments of the invention prioritize effective crystalhabit modification in the selection, preparation, and application oftreatment additives.

Crystal growth is dynamic. Crystalloids (forming crystal lattices) thatdo not grow properly tend to re-dissolve. Treatment additives, asdiscussed above, can modify the size and shape of mineral crystalhabits. Crystal habit modification is a significant basis for improvedtreatment of aqueous systems. In fact, crystal habit modification itselfcan yield improved performance in other scale control mechanisms.Crystal modification is a mechanism that facilitates thesub-stoichiometric action of threshold inhibition. Crystal modificationis also an in-situ mechanism that prevents or reduces particle cohesion,resulting in reduced deposition tendency. Crystal modificationadditionally produces distortions in crystalline surface or latticestructure that limit surface-to-surface contact area, thus limitingpotential adhesion. Further, what is recognized as stabilization and, insome cases, dispersion, can also be enabled or enhanced by thefunctionality of crystal habit modification. Thus, through betterunderstanding of how polymer additives act to modify crystal habit,enhanced additive performance across several scale control mechanismscan be realized, yielding enhanced overall performance.

When designing or selecting a polymer for mineral scale control, it isimportant to recognize the desired primary functionalities, their impactupon scale control efficacy, and nuances that may enhance overallperformance. Polymers can be particularly sensitive to a wide range ofdesign factors, including for example composition, molecular weight,molecular weight distribution, polymer end-groups, and the manufacturingor polymerization process utilized. Each of these considerations canhave substantial consequences upon overall performance, the emphasizedfunctional feature (e.g., threshold inhibitor, dispersant, crystalmodifier), the polymer’s stability and retained performance in severeservice conditions, and the type of mineral scale or deposit the polymerwill control.

In an embodiment of the invention, crystal habit modification isprioritized as a primary functionality of potential polymer additivesfor treating aqueous systems. FIG. 2A illustrates a typical view ofpolymer functionality, in which each of the six scale control mechanismsdescribed above are viewed discretely, and one or more mechanisms may beselected as a primary treatment focus. While it may be common for someproducers or sellers of treatment additives to make broad claims for aproduct’s functionality across most or all of these mechanisms, askeptical purchaser or user of such products often has come to view eachone as a single-purpose additive. Thus the interrelationships offunctional mechanisms for polymer additives may be easily overestimatedor underestimated. FIG. 2B depicts a re-alignment of focus on thesefunctional mechanisms, prioritizing crystal habit modification as afirst-order concern in treating aqueous systems.

As illustrated in FIG. 2B, the mechanisms enabling polymer additivefunctionalities are to a large degree interconnected. Overall scalecontrol can be better achieved by employing multiple mechanismssequentially or simultaneously. To illustrate this, using for example acarboxylated homopolymer such as polymaleic acid to control calciumcarbonate scaling, all six scale control functionalities are likelyrelevant to the scale management process. Sequestration could be aninitial interaction employed between the polymaleic acid and calciumcarbonate. As illustrated in FIG. 3A, in the sequestration line ofdefense, the polymer 100 is sequestering calcium ions 200 such that thecalcium ions 200 are unavailable for combination with carbonate ions300. By definition, chelation is also employed here. The carboxylic acid(H—O—C═O or COOH) functional groups 110 along the backbone of polymer100 carry a minus one charge. Because of this, two carboxylic acidgroups 110 are required to fully sequester each divalent (2+) calciumion 200. It is this coordination of the polymer 100 at two sites alongthe molecule with the calcium ion (central metal ion) 200 that meets theformal definition of chelation.

The functionality of sequestration and chelation by such polymers istypically temporary in process water treatment applications such ascooling towers and boilers. The duration (how long?) and extent (howmuch?) the polymer can maintain solubility of calcium in an environmentwhere carbonate species is present is dependent upon many factors,including the concentration of the scale forming ions (in this case[Ca²⁺][CO₃ ²⁻]), pH, temperature, polymer concentration, polymerefficacy (design), presence and concentration of suspended solids,presence and concentration of other soluble ions, the rate in which thewater (and its impurities) are concentrated, and the frequency ofpolymer addition.

FIG. 3B illustrates that as calcium carbonate 400 begins to precipitatein this example, it is necessary for the polymer 100 to interact withboth the soluble calcium 200 that remains in solution (sequestration,chelation) and also the forming crystal lattices 400, which aresometimes referred to as crystalloids. These calcium carbonatecrystalloids 400 can be thought of as “pre-crystals” as they have begunto form crystal lattices that are necessary for formation of macro,insoluble calcium carbonate scale. However, these crystalloids 400 areconsidered soluble or, at least, at the verge of precipitation andhighly vulnerable to re-solubilization. In this case, the polymer 100can begin to exhibit stabilization functionality. The polymer 100 maynot be able to fully sequester all the calcium ions 200 that arepresent, nor may it be able to prevent formation or repeated dissolution(partial threshold inhibition mechanism) of crystalloids 400, but it maybe effective in preventing growth of the crystalloids beyond the size ofcolloidal particles.

A key determinant in the functionality of threshold inhibition is asub-stoichiometric relationship between the level of polymer and thescale forming species. A strict mechanism of sequestration and/orchelation would not allow for this relationship. Rather, a process ofpartial and/or temporary sequestration, formation of the crystalloid,and re-dissolution of the interrupted crystal lattice formation isnecessary to accomplish this phenomenon at sub-stoichiometric ratios.With reference again to FIG. 3B, through the process it can beenvisioned that the polymer 100 is fighting a battle on two fronts: thewater soluble battle with divalent calcium 200 and the water insolublebattle against calcium carbonate crystalloids 400. As it has beendefined, threshold inhibition is a temporary effect. Thus, the polymer100 can be understood to be winning and losing each of these battlessimultaneously until bulk precipitation occurs. The polymer 100essentially wins as it sequesters divalent calcium ions 200 (watersoluble battle) and as it adsorbs onto crystalloid surfaces 400 (waterinsoluble battle) disrupting crystal lattice formation. The effectiveconcentration of polymer 100 is constantly being depleted as the polymerwages war on both fronts. However, as crystalloids 400 re-dissolve, thepolymer 100 too is freed to continue the battle on the water solublefront with calcium ions 200. This process is continued up to the pointat which crystalloids 400 tend to form lattices 500 that do notre-dissolve, where larger macro-structures of calcium carbonate form,and bulk precipitation occurs. Again, the rate and duration of thispolymer-calcium carbonate war is dependent upon a variety of factors,including several previously mentioned. Threshold inhibition is anunusual event that is somewhat specific to certain polymers andphosphonates. Other materials that can have much stronger sequesteringor chelating properties or a much higher affinity for adsorption ontoforming calcium carbonate do not exhibit threshold inhibitionproperties.

Once bulk precipitation has occurred, the two remaining mechanisms formineral scale control may be employed. Dispersion is perhaps the simplerof the two, although nuances exist here. It is important to separate theconcept into two pieces: in-situ dispersion and post-precipitationdispersion. In both cases, the polymer is effective in maintaining asuspension (dispersion) in solution by electrostatic repulsion. In eachcase, the polymer interacts both with the precipitate and with otherpolymer molecules to prevent agglomeration and resultant separation fromsolution. However, in some cases, where the polymer is present in-situ,another benefit can be employed. If the polymer is effective inmodifying or distorting crystals as precipitation occurs, those crystalsare much less likely to cohere to other crystals and thus are much moreeasily dispersed. Polymaleic acid is a known example of this in-situmechanism. Polymaleic acid is actually rather poor at suspending solidsdue to its very low molecular weight (typically 500-800 Daltons). Incontrast, polymaleic acid is rather effective at preventingagglomeration of solids such as calcium carbonate when it is present asa crystal habit modifier during the precipitation process.

The ability of a polymer to modify the crystal habit of mineral scalesis known in the art. Folklore suggests that prior to the invention ofsynthetic polymers for this purpose, starch (a naturally occurringpolymer) from potatoes was utilized to soften scale in the boilers ofsteam locomotive engines. More recently, synthetic polymers such aspolycarboxylates (polyacrylic acids, polymaleic acids), sulfonatedcopolymers, and various other polymers have been used specifically forthis purpose in a variety of water treatment applications. The conceptof crystal habit modification is simple and qualitative. Essentially,the expectation for the polymer is to adsorb onto the surface of aforming crystal lattice, impede the directional growth of the lattice,and subsequently promote the formation of precipitated crystals that areabnormal in shape, size, and overall appearance.

This can be illustrated in FIGS. 4A-4D. FIG. 4A shows athree-dimensional illustration of a forming crystal lattice 500 where apolymer 100 begins to adsorb onto the lattice surface. It can beobserved in FIG. 4B how this adsorption of the polymer 100 inhibitsdirectional growth of the forming crystal lattice 500 in severaldimensions or directions 550. The directional growth inhibition thenleads to one of two events with the forming crystal lattice 500. Thelattice 500 is either unstable, such that it tends to re-dissolve (FIG.4C) as crystalloids 400, or bulk precipitation occurs and crystal habitmodification of the bulk precipitate 600 is observed (FIG. 4D). FIGS.5A-5B illustrate the benefit of crystal habit modification in the bulkprecipitate 600, which now exhibits fewer planar crystal surfaces withlower overall planar surface area. The effect is improved scalemanagement performance, even as precipitate 600 potentially interactswith, e.g., a metal surface 700 or a tube or pipe interior 750.

When designing a polymer for mineral scale control, it is important torecognize the desired primary functionalities, their impact uponefficacy, and nuances that might enhance overall performance. Polymerscan be particularly sensitive to a wide range of design factors. Amongthese are considerations such as composition, molecular weight,molecular weight distribution, polymer end groups, and the manufacturingor polymerization process utilized. Each of these considerations canhave substantial consequences upon overall performance, the emphasizedfunctional feature (threshold inhibitor, dispersant, crystal modifier,etc.), the polymer’s stability or retained performance in severe serviceconditions, and the type of mineral scale or deposit the polymer willcontrol. Some insights as to how composition relates to functionalityare provided in the table FIG. 6 , where it can be observed that acarboxylate group, such as from acrylic acid and maleic acid, canprovide the basis of functionality for calcium carbonate and calciumsulfate. Further, sulfonate groups can provide functionality for calciumphosphate, iron, and zinc stabilization. Non-ionic groups are typicallyutilized to enhance polymer performance by increasing interaction with aparticular surface. Examples of this include the addition of a non-ionicto enhance calcium carbonate crystal modification properties, improvecalcium phosphate and iron stabilization, or to add a viable interfaceto organics or biomass. The implications of molecular weight can beoversimplified to generalize that lower molecular weight (<3,000Daltons) polymers tend to provide better threshold inhibitionproperties, while polymers with an average molecular weight between5,000 and 10,000 Daltons tend to function better as stabilizers andparticulate dispersants. Of course there are exceptions to these rulesof thumb but they largely hold true throughout the range of polymerscommonly offered to industry. Other aspects such as the polymerizationprocess, end-group selection, and molecular weight distribution can havea tremendous impact upon polymer performance as well. One good exampleof this is the use of hypophosphite in the preparation of polyacrylates.These polymers are known as phosphinocarboxylates but, more accurately,they are polyacrylates prepared using sodium hypophosphite. Thesepolymers are known to have better thermal stability and tolerance toiron and salts than typical polyacrylates prepared by more conventionalmethods.

Thus, an embodiment of the invention prioritizes effective crystal habitmodification in the selection, preparation, and application of treatmentadditives. Focusing on effective crystal habit modification yieldscorollary benefits in other mechanisms of functionality, and can providebetter overall scale management performance than prioritizing thresholdinhibition or other mechanisms.

In further embodiments, improved copolymer additives are specified toachieve improved crystal habit modification performance, and corollarybenefits.

The use of polymaleic acid (PMA) for calcium carbonate scale control hasbeen known for many years, since approximately the 1920′s. German,British, and American scientists seemingly recognized the potentialefficacy and commercial benefits of PMA in similar time periods.Widespread industrial use of PMA began in the 1970′s and continues inthe present. PMA is known, accepted, and utilized for the treatment ofwater and, in particular, the control of calcium carbonate. Further, PMAhas become a leading choice for service companies seeking an effectiveadditive for severe service applications in cooling waters, boilers,oilfield operations, large-scale thermal desalination activities, andvarious other uses.

In an embodiment of the invention, improved copolymers with certainsimilarities to PMA exhibit improved performance in several aspects, ascompared to PMA and also to mono-carboxylic acid polymers such aspolyacrylic acid. For example, improved copolymers according to theinvention can exhibit improved stability in harsh water conditions,improved crystal habit modification performance for calcite (a cubicform of calcium carbonate), and highly effective calcium carbonatethreshold inhibition in harsh waters. In contrast to mono-carboxylicpolymers such as polyacrylic acid, the stability of such improvedcopolymers in harsh water systems is enhanced due to the presence andproximity of di-carboxylic acid groups along the copolymer backbone. Thenegative charge inherent within each carboxylic acid functional groupprovides effective repulsion along the backbone of the copolymer. Thiselectrostatic repulsion, in turn, provides rigidity and stability alongthe copolymer that reduces the incidence of it coiling or collapsingupon itself as it encounters high levels of hardness or salinity in anaqueous environment. This comparison is illustrated in FIGS. 7A-7B. Thecontinued extension of the copolymer conformation in harsh waterenvironments (FIG. 7A) provides that the copolymer not only remainsstable (soluble) in such conditions, but also retains its functionalproperties. This is in contrast to polymers such as polyacrylic acid (inFIG. 7B), which can lose both solution stability and efficacy incomparable environments.

Modification of calcium carbonate crystals is of increasing importancein modem water treatment applications. Beyond providing an underlyingmechanism that enables threshold inhibition, as described above, crystalmodification itself can be a primary functionality controlling mineralscale deposition in failure situations. Industry initiatives such aswater conservation, use and reuse of poorer quality make-up water, andelimination of phosphorous tend to increase the likelihood of bulkprecipitation and the ultimate formation of deposited mineral scale.Enhanced copolymers according to the invention can exhibit markedlyimproved crystal modification properties for calcite, compared to knownindustry products such as PMA and Multifunctional One Polymers (MOP).

Experimental observation and testing can demonstrate the effects ofpolymers as crystal habit modifiers. For example, experimentalobservations to evaluate relative crystal modification properties ofPMA, MOP polymers, and enhanced copolymers according to the inventionshow improvements achieved at 15 mg/l and 30 mg/l treatment dosagesrelative to a blank sample with no polymer treatment. Since PMA, MOP,and enhanced copolymers each can be effective threshold inhibitors insevere conditions, laboratory work was performed under conditions thatwould ensure precipitation occurred, and crystal modification propertiescould be observed. 50 ml of a solution containing 1200 mg/l of Ca²⁺(using CaCl_(2y)•2H₂O) was treated with the designated polymer dosage.Using Na₂CO_(3•)H₂O, 50 ml of a 1200 mg/l solution of CO₃ ²⁻ was thenadded to the Ca²⁺, polymer-dosed solution. Additional solutionscontained 600 mg/l of Ca²⁺ and 600 mg/l of CO₃ ²⁻. Each solution wasmeasured to have a pH of 9.5 to 10.2 and was heated in a water bath at70° C. for 18 hours. The samples were allowed to cool and theprecipitate was collected using a plastic transfer pipette, and sampleswere examined by both compound and Scanning Electron Microscopy (SEM)using a Hitachi S-4700 Type II cold field emission SEM. The tabledepicted in FIG. 8 details the severe service conditions of theexperiments. The exclusive formation of calcite is represented in FIGS.9A-9B for the blank (no polymer treatment). Similarly, the SEMmicrographs represented in FIGS. 10A-10B reveal that experimentalconditions produced a uniform calcite (cubic calcium carbonate)precipitate.

As noted, in the treatment industry PMA is a widely recognized crystalhabit modifier to cubic calcium carbonate (calcite.) As can be observedin FIG. 11A-11 d , with PMA both polymer dosages “soften” the calciteand begin showing modifications features. Yet the presence of unmodifiedcalcite is prominent in the 15 mg/l dosage (FIGS. 11A-11B) and is stillobservable at the 30 mg/l treatment level (FIGS. 11C-11D). At bothdosages, the crystal modification achieved by PMA manifests as a“boulder” type shape.

Multifunctional One Polymers (MOP) are relatively newer polymers whichare designed for multiple-use purposes rather than specific performanceas crystal habit modifiers. FIGS. 12A-12D show that MOP does notdemonstrate the same level of crystal modification as compared to PMA inFIGS. 11A-11D. At both the 15 mg/l and 30 mg/l dosages, the MOP-treatedsamples retain much of their original, untreated cubic form. A potentialexplanation for this could be the polymer architecture and design.Typical MOP materials are 2,000-3,000 Mw and contain sulfonatedmonomers. These design features may limit the interaction of the polymerwith forming calcite crystalloids and thus reduce the overall level ofobserved crystal habit modification.

As represented in FIGS. 13A-13D, the degree, type, and quality ofcrystal distortion observed with an enhanced copolymer in accordancewith the invention were unusual, unexpected, and unmatched by either thePMA or MOP polymers. Distinctive to such enhanced copolymers is theformation of spherical and rounded pill-shaped macro structures. Suchstructures are less likely to form strong adhesions onto metal surfaces,and require less mechanical energy to remove when they are deposited(see FIGS. 5A-5B). Remarkably, it can be observed that an enhancedcopolymer even shows a greater degree of crystal distortion at lowertreatment levels. FIGS. 13A-13B show an enhanced copolymer at a dosageof 15 mg/l, with resulting crystal distortion of over 50% of thepotential cubic macro-lattices. Further, FIGS. 13C-13D show widespreadcrystal distortion of potential cubic macro-lattices at the 30 mg/ldosage.

Targeted crystal habit modification performance, as discussed above, canalso yield improved performance in related functional mechanisms ofscale management. A comparison of PMA and an enhanced copolymer inaccordance with the invention, as threshold inhibitors, was conductedusing a “Severe Calcium” laboratory bottle testing method, with theresults summarized in the chart depicted in FIG. 14 . In this method, 50ml of a solution containing 1200 mg/l Ca²⁺ was added to a French squarebottle and treated with the indicated polymer dosage (as active). Then50 ml of solution containing sodium carbonate (150 mg/l as CO₃ ²⁻),sodium bicarbonate (450 mg/l as CO₃ ²⁻), and a borate buffer (98 mg/lB₄O₇ ²⁻) was added to the calcium/polymer solution. All samples had ameasured pH of -9.0 and were capped and placed in a water bath at 50° C.for 18 hours. The Langelier Saturation Index was calculated to be -3.0.In this evaluation, PMA and the enhanced copolymer were compared acrossincreasing dosages of 5, 10, 15, and 30 mg/l on an active polymer basis.Within this severe calcium test, the enhanced copolymer demonstratesgood stability in harsh conditions (high calcium, high alkalinity) andshows strong functionality as a threshold inhibitor, with better resultsthan PMA at the lower treatment levels and slightly lower results at the30 mg/l dosage. The inherent limitations of bottle testing for calciumcarbonate inhibition and the small sampling of data suggest that moretesting should be performed to evaluate boundaries of the enhancedcopolymer’s performance as a threshold inhibitor. As with PMA or anyother inhibitor of this type, it may be recommended that such enhancedcopolymers be formulated with PBTC (preferred) or HEDP to furtherenhance threshold inhibition functionality. A recommended ratio maybe3:l copolymer to PBTC with a typical delivery 10 mg/l active polymerand 3 mg/l active PBTC as a starting point for many applications.

In an embodiment of the invention, an enhanced copolymer is preparedin-situ as a substantially maleic acid copolymer by polymerizing maleicacid monomer components. The maleic acid monomer components aretransformed into monomeric repeating units within each polymer molecule.Preferably, this is aqueous polymerization, a process known in the art,which may provide various advantages such as being more economical thanalternate methods of polymerization, yielding a polymer with loweraquatic toxicity, etc. An additional and previously under-appreciatedadvantage of aqueous polymerization is that it can provide a superiorenvironment for beneficial in-situ copolymerization, such as producingimproved copolymers exhibiting superior crystal habit modificationproperties. Contrary to common practice and understanding, rather thanattempting to minimize decarboxylation during the polymerizationprocess, there is preferably an effort to increase decarboxylation. Thismay be achieved, e.g., by changing various process parameters such asreaction temperature, the concentration of metal catalyst used, theconcentration of hydrogen peroxide used, or adjusting other reactionadditives. A result of increased decarboxylation is that, during thepolymerization process, some of the maleic acid monomer componentsbecome non-carboxylated monomeric repeating units of the polymer beingformed, resulting in an in-situ created copolymer rather than asubstantially pure homopolymer. Preferably the process also gives riseto terminal hydroxyl groups in the copolymer.

Thus, the copolymer includes a quantity of non-functionalized groupswhich may, in application, aid in the adsorption of the polymer onto acrystal surface. An enhanced polymaleic acid copolymer prepared in sucha manner may preferably include mono-carboxylic acids, non-ionicfunctional groups, and terminal hydroxyl groups in proportions toachieve the desired treatment functionalities. For example, such acopolymer may include at least approximately 10% (Mw) polymaleic acidand at least approximately 10% (Mw) of in-situ formed co-monomers,including at least 10% (Mw) decarboxylated maleic acid.

FIGS. 15 and 16 are nuclear magnetic resonance (NMR) spectrographscharacterizing the chemical properties of two polymer additives.Comparing FIG. 15 (prior art) with FIG. 16 (enhanced copolymer) shows asignificantly higher proportion of decarboxylated monomeric repeatingunits in the enhanced copolymer. In illustrative preferred embodimentsof the enhanced copolymer described in FIG. 17 , with molecular weightof the combined copolymer between 300 and 3,000 Daltons, copolymerconstituent proportions are specified as follows:

-   Maleic Acid is present at over 50 molar %-   Maleic Anhydride may be present at up to 5 molar %-   Acrylic Acid is present at up to 50 molar %-   a 2-carbon alkane group is present at up to 50 molar %

A copolymer prepared in accordance with the principles disclosed herein,or characterized by the attributes disclosed herein, as a furtherembodiment of the invention may then be applied to an aqueous system asa treatment additive to prevent or remediate mineral scaling. Inapplication, the copolymer may, among other functionalities, adsorb ontocrystalloid or crystal lattice structures, with a result of modifyingthe crystal habit of, e.g., an undesirable inorganic compound. Someexamples of such compounds include calcium carbonate, calcium sulfate,barium sulfate, calcium oxalate, calcium phosphate, silica, orsilicates.

Composition components (supplied or produced in-situ duringpolymerization) used in preparing an improved copolymer in accordancewith embodiments of the invention may be selected and adjusted in ratiosintended to optimize a single functional mechanism for scale control(preferably the mechanism of crystal habit modification), or to achievea desired balance of multiple mechanisms. For example, ratios ofcarboxylates, sulfonates, and non-ionic compounds may be adjusted sothat the ratio of non-ionic compounds is selected to optimize polymeradsorption on crystal surfaces, while the ratios of carboxylates andsulfonates are selected to retain adequate threshold inhibition,chelation, and sequestration properties of the copolymer additive.

Many modifications or expansions upon the invention and the variousillustrative embodiments described in this application still fall withinthe spirit and scope of the invention, and should be so considered.

1. A method of preparing in-situ a substantially maleic acid copolymer,comprising: polymerizing at least a portion of a plurality of maleicacid monomer components, wherein some of such maleic acid monomercomponents are transformed into monomeric repeating units within each ofa plurality of polymer molecules, increasing decarboxylation during saidpolymerizing, forming in-situ a copolymer molecule comprising at leastone decarboxylated portion of said copolymer molecule, increasing anaverage frequency of non-carboxylated monomeric repeating units in saidpolymer molecules to at least approximately 5 molar%.
 2. A methodaccording to claim 1, wherein said polymerizing comprises aqueouslypolymerizing.
 3. A method according to claim 2, wherein said increasingdecarboxylation comprises adjusting one or more reaction parametersselected from the group of temperature, metal catalyst concentration,hydrogen peroxide concentration, and other reaction additives.
 4. Amethod according to claim 2, wherein said copolymer molecule furthercomprises at least one terminal hydroxyl group.
 5. A method according toclaim 3, wherein said polymerizing further comprises co-polymerizing oneor more co-monomers capable of reacting in a free-radical aqueouspolymerizing system. 6-17. (canceled)